Strain control of Morin temperature in epitaxial α-Fe2O3(0001) film

Abstract

We present comprehensive studies of strain effects on the spin reorientation transition (SRT), the so-called Morin transition, in α-Fe2O3(0001) films. The α-Fe2O3(0001) epitaxial films were grown with a Cr2O3 buffer layer on Al2O3(0001) substrates through an oxide molecular beam epitaxy. The antiferromagnetic spin axis was monitored by using the Fe L2-edge X-ray magnetic linear dichroism. The buffer layer was found to introduce compressive strain into the α-Fe2O3(0001) film due to its 1.6% smaller in-plane lattice constant. The degree of strain is monotonically reduced with the increase of the α-Fe2O3 film thickness and becomes relaxed in the thick region (> 20 nm). The transition temperature TM, which increases up to ≃360 K, well above the bulk TM = 263 K, for the film thickness ≃3 nm, gradually decreases as the film thickness increases. We also examined the Néel temperature TN in the ultra-thin region (< 3 nm), which rapidly drops with the decrease of the film thickness. The correlation between TM and the strain in the α-Fe2O3(0001) epitaxial films was found to be well explained in terms of two competing energies of magnetic dipole anisotropy and single-ion magnetocrystalline anisotropy except for the ultra-thin region, in which TN is dominated by the finite-size effects.